The two neurophysin carrier proteins which are made by cells in the supraoptic nucleus of the hypothalamus are synthesized as parts of larger precursor molecules. Thyrotropin releasing hormone (TRH) is present in high concentrations in the hypothalamus. It can be released from hypothalamic synaptosomes by depolarization with K ion in the presence, but not the absence, of Ca ions. TRH is also found in the retina. The level of TRH increases when animals are exposed to light and decreases when they are placed in the dark. ACTH has been shown to be present throughout the brain. It is found in particularly high concentrations in limbic structures, where its levels are not altered by hypophysectomy. The regional distribution of beta lipotropin, beta endorphin, neurotensin, substance P, TRH, somatostatin, and glutamic acid decarboxylase have been studied. BIBLIOGRAPHIC REFERENCES: Brownstein, M.J., Arimura, A., Fernandez-Durango R., Schally, A.V., Palkovits, M. and Kizer, J.S.: The effect of hypothalamic deafferentation on somatostatin-like activity in the rat brain. Endocrinology 100: 246-249, 1977. Gainer, H., Sarne, Y. and Brownstein, M.J.: Neurophysin biosynthesis: Conversion of a putative precursor during axonal transport. Science 195: 1354-1356, 1977.